From birth, when babies' fingers instinctively cling to those of adults, their bodies and brains seek an intimate connection - a bond made possible by empathy, the remarkable ability to love and to share the feelings of others.

The Navy has the SEALS, and the Army has the Green Berets. They are masters of asymmetrical warfare, trained to immerse themselves in hostile territory, sleeping near their enemies and building relationships with people who may want to kill them.